1. Technical Field
The present invention relates to a liquid detecting apparatus that drives a liquid detecting unit so as to detect the presence or absence of a certain amount of liquid. In addition, the present invention further relates to a liquid ejecting apparatus that is provided with such a liquid detecting apparatus.
2. Related Art
A technique for detecting the presence or absence of a certain amount of liquid that is contained in a liquid container, an example of which is ink contained in an ink cartridge, is known in the technical field of a liquid detecting apparatus to which the present invention pertains. In the above-described technique for detecting the presence/absence of a certain amount of liquid contained in a liquid container of the related art, a piezoelectric element is used as a liquid detection sensor. In the related-art liquid detection technique, either the presence or absence of a certain amount of liquid such as ink is detected by means of, or, in other words, on the basis of, the waveform of a counter-electromotive voltage (i.e., back electromotive voltage) that is obtained after the piezoelectric element has been driven. More specifically, the liquid detecting apparatus of the related art detects the presence or absence of a certain amount of ink as follows. In the configuration of the liquid detecting apparatus of the related art, an ink flow channel is formed in the proximity of a piezoelectric element. The piezoelectric element generates residual vibration after application of a voltage thereto, and outputs an output signal as a result of the residual vibration. The liquid detecting apparatus of the related art makes a judgment as to whether a frequency that is obtained on the basis of the waveform of the output signal that was output as a result of the residual vibration agrees with one resonance frequency that is obtained under the conditions that the ink flow channel that is formed in the proximity of the piezoelectric element is filled with ink or another resonance frequency that is obtained under the conditions that the ink flow channel that is formed in the proximity of the piezoelectric element is not filled with ink. Then, on the basis of the result of the above-described judgment, the liquid detecting apparatus of the related art makes a further judgment as to whether the amount of ink that is contained in an ink cartridge is larger than, or, at the smallest, equals to, a predetermined threshold amount or not. An example of the ink detection technique of the related art explained above is disclosed in JP-A-2001-146030.
In a case where a driving circuit that drives a piezoelectric element is provided as a discrete driver that is separated from the piezoelectric element in order to obtain the waveform of a counter-electromotive voltage, there arises a problem in that the electrodes of the piezoelectric element are highly vulnerable to exogenous noise because the output impedance of the piezoelectric element is high. As an approach to address such a problem, it is possible to modify and thus improve the structure of an ink cartridge so as to reduce, suppress, or completely cancel and reject any exogenous noise. However, such a solution will inevitably make the manufacturing of an ink cartridge more complex, thereby, for example, increasing the number of manufacturing steps. Or, as another non-limiting disadvantage of such a solution, it will increase the cost of production thereof.